Moog Crossbow NAV440 Series - Manual (Page 28)

Page 28
NAV440 User Manual
7430‐0131‐01 Rev. F
The first phase of operation is the high‐gain initialization phase. During the initialization phase, the unit is expected
to be stationary or quasi‐static so the EKF weights the accelerometer gravity reference and Earth’s magnetic field
reference heavily in order to rapidly estimate the X, Y, and Z rate sensor bias, and the initial attitude and heading of
the unit. The initialization phase lasts approximately 60 seconds, and the initialization phase can be monitored in
the software Status BIT transmitted by default in each measurement packet. After the initialization phase, the unit
operates with lower levels of feedback (also referred to as EKF gain) from the accelerometers and magnetometers to
continuously estimate and correct for roll, pitch, and heading (yaw) errors, as well as to estimate X, Y, and Z rate
sensor bias.
The AHRS440provides the same scaled sensor and angle mode packets of the VG440. The AHRS440 defaults to the
A1 Angle Packet which outputs the roll angle, pitch angle, yaw angle, and digital IMU440data. In the AHRS440, the
A0
and A1 packets contain accurate magnetometer readings. Refer to Chapter 9. Communicating with the 440 and
Chapter 10. Programming Guidelines for full packet descriptions.
NOTE: For proper operation, the unit relies on magnetic field readings from its internal 3‐axis magnetometer. The
unit must be installed correctly and calibrated for hard‐iron and soft iron effects to avoid any system
performance degradation. Refer to Chapter 4. Magnetometer Calibration and Alignment Guidelines for
information about magnetic calibration; review that information before using the AHRS440.
NOTE: The unit must be mounted at least 24” away from large ferrous objects and fluctuating magnetic fields.
Failure to locate the unit in a clean magnetic environment will affect the attitude solution.
AHRS440 Advanced Settings
In addition to the configurable baud rate, packet rate, axis orientation, and sensor low‐pass filter settings, the unit
provides additional advanced settings which are selectable for tailoring the unit to specific application
requirements. The AHRS440 advanced settings are listed in below: Table 7
Table 7AHRS 440 Series Advanced Settings
Setting Default Value Comments
Baud Rate 38400 9600, 19200, 57600 also available
Packet Type A1 S0, S1, S2, A0, A2, N0, N1 also available
Packet Rate 25 Hz This setting sets the rate at which selected Packet Type, packets are output. If
polled mode is desired, then select Quiet.
Orientation See Figure 4 on
page 22. To configure the axis orientation, select the desired measurement for each axis:
NAV‐VIEW 2.2 will show the corresponding image of the unit, so it easy to
visualize the mode of operation. Refer to Orientation Field on page 84 for the
twenty four possible orientation settings. The default setting points the
connector AFT.